1. Field of the Invention
This invention is related to weaving of multilayer products woven from columns of warp fibers controlled by heddle columns. In particular, the ratio of the number of warp columns to the number of heddle columns is a fractional number.
2. Description of the Related Art
The use of reinforced composite materials to produce structural components is now widespread, particularly in applications where their sought desirable characteristics are being light in weight, strong, tough, thermally resistant, self-supporting and adaptable to being formed and shaped. Such components are used, for example, in aeronautical, aerospace, satellite, recreational use (as in racing boats and autos), and other applications.
Typically such components consist of reinforcement materials embedded in matrix materials. The reinforcement component may be made from materials such as glass, carbon, ceramic, aramid, polyethylene, and/or other materials which exhibit desired physical, thermal, chemical and/or other properties, chief among which is great strength against stress failure. Through the use of such reinforcement materials, which ultimately become a constituent element of the completed component, the desired characteristics of the reinforcement materials, such as very high strength, are imparted to the completed composite component. The constituent reinforcement materials may, for example, be woven into multilayer preform structures.
Weaving has been employed for many centuries to create woven structures. Woven structures are formed by interlacing threads, yarns, or fibers that fall into two categories: (i) the “warp threads”, yarns, or fibers that are parallel to the selvedges, or edges, (sometimes called machine direction or MD) and which are interlaced or “woven,” with (ii) a perpendicular series of “weft threads”, yarns, or fibers (sometimes called cross-machine direction or CD). Typically, the warp and weft yarns or fibers are interlaced to make a woven structure on a weaving loom. The simplest weave pattern consists of an alternating pattern where each weft thread, yarn, or fiber passes successively above and below a warp thread or fiber. More complex structures are woven in three dimensions (3D weaving) such that additional yarns bind the warp and weft yarns in multilayer structures.
Customarily, weaving looms employ three primary motions within the weaving process: i) shedding, (ii) picking, and (iii) beating-up. Shedding involves forming a triangular opening between groups of warp fibers for the passage of weft fibers by a shuttle, for example. Picking involves passing the weft fiber through the shed. And beating-up involves using a comb-like reed to pack the weft fibers as close as desired to each other in a repeating weave pattern.
Commonly, in Jacquard weaving, the weaving component that is used to separate warp fibers, and form the shed, or triangular opening or space through which the weft fiber can pass, is called a heddle. Control of the vertical position of the heddles controls the formation of the shed. The shed opening may be formed by lifting one set of warp fibers relative to another set. Alternatively, one set of fibers may be lifted from a neutral position and the remaining fibers lowered from the same neutral position. In some cases, alternating warp fibers are lifted with respect to adjacent fibers. Or a number of consecutive fibers are lifted together, or are not raised, to form a desired pattern with the weft fibers in the woven structure.
Usually, heddles are elongated structures made from metal, wire, twisted wire, polymeric braid, pressed sheet metal, polyester, or string with an appropriately sized eye, or opening, through which a warp fiber is passed through. The top and bottom of the heddles have structures that allow them to be attached, connected, or mounted to a component called the heddle harness or heddle column. By and large, warp fibers extend from a warp beam, or warp creel, on one end of the loom, pass through a heddle, and attach to another beam, or fabric column, at the other end of the loom. After the weft fibers are passed through the shed formed by the warp fibers, a reed is used to beat up, or tighten the weft and warp fibers into the desired pattern and density.
One characteristic of woven structures is the number of warp fibers per inch of woven-material width. In weaving terminology, the number of warp fibers per width-wise inch is known as dents per inch or “dpi.” For example, a woven structure with 12 warp fibers per width-wise inch would be referred to as a 12 dpi material.
Normally, the weaving loom has suitable heddle-column geometry that was chosen for the woven structure being produced. By way of exemplary illustration, if the woven structure being produced is to have 12 dpi, the heddle column may have 12 heddles per inch. Because each warp yarn passes through one heddle, the dpi of the woven material determines the number of heddles per inch width, or heddle spacing, on the heddle column.
Typically, woven structures to be used for preforms are multilayer 3D structures. That is, when viewed from a horizontal plane, multiple layers of warp ends can be found. For example, in a 32-layer woven structure, there would be 32 warp ends through the thickness of the material when viewed from a horizontal cut. These warp fibers are usually arranged in columns such that a 32-layer woven structure would have 32 warp fibers per warp column.
When weaving a multilayer structure for a preform, the weaving apparatus geometry may be selected such that the heddle-column spacing can be multiplied by a whole number to achieve the desired warp-column spacing. For example, if a 32-layer preform with 12 warp fibers per width-wise inch, or dpi, were desired, the weaving apparatus could have a heddle column with 32 heddles where the heddle spacing would be 12 heddles per inch. As such, fibers on one warp column would be laced through heddles on one heddle column. Alternatively, a heddle column with 64 heddles where the heddle spacing would be 6 heddles per inch may be used. With 64 heddles per column, fibers on two warp columns would be laced through heddles on a heddle column. In some circumstances of multilayer woven structures with high warp fiber counts, configuring the weaving apparatus where one heddle column would weave one warp column can have too much warp and weft fiber congestion to weave efficiently. When configuring the weaving apparatus where one heddle column would weave two warp columns, the depth of the heddles is large so that a very small shed opening may be formed, resulting in poor warp control and difficulties in weaving.